1. Technical Field of the Invention
The present invention pertains in general to lightguides for backlighting of keypads and liquid crystal displays, and more particularly, to diffusor structures which are incorporated into lightguides.
2. Description of Related Art
Keypads and liquid crystal displays commonly utilize a lightguide to transmit light across the liquid crystal display or keypad from a light source. In order to diffuse the light evenly, defusing structures are incorporated into the lightguide. The most common method for incorporating diffusing structures into the lightguide is to print diffusor dots or diffusor patterns onto a rear surface of the light guide. Typically, a screen printing process or pad printing process is used to print the diffusor dots or patterns directly onto the rear surface of the lightguide. The pad printing and screen printing processes have limitations as to the resolution of the diffusor patterns which can be printed and also limit the surface topography of the lightguide on which the patterns can be printed. For example, feature sizes must be at least 0.004 to 0.006 inches in size using the screen printing process and even larger for the pad printing process. Furthermore, these processes may not be used on surface topographies having confined areas, such as recesses, or on areas with adjacent features such as pins. Moreover, these processes can not be used on lightguides having significantly contoured non-planar surfaces.
The resolution limitations imposed by the pad printing and screen printing processes create another problem for backlighting of liquid crystal displays and keypads. In order to achieve uniform and efficient illumination across the entire length of the lightguide, diffusor patterns need to be small in size and low in density near the light source where light is abundant and increasingly larger in size and more dense the further the distance from the light source. In certain circumstances, the screen printing and pad printing processes cannot achieve the resolutions required for uniform backlighting. The result is the creation of localized bright spots. To address this problem, additional diffusers constructed out of textured or frosted Mylar are located between the lightguide and the display.
It would be advantageous, therefore, to create a lightguide incorporating a diffusor structure which overcomes the resolution and typography limitations associated with the pad printing and screen printing processes.